The present invention relates to computed tomography (CT) imaging apparatus; and more particularly, to the acquisition of multiple slices with a linear detector array.
In a computed tomography system, an x-ray source projects a fan-shaped beam which is collimated to lie within an x-y plane of a Cartesian coordinate system, termed the "imaging plane". The x-ray beam passes through the object being imaged, such as a medical patient, and impinges upon an array of radiation detectors. The intensity of the transmitted radiation is dependent upon the attenuation of the x-ray beam by the object and each detector produces a separate electrical signal that is a measurement of the beam attenuation. The attenuation measurements from all the detectors are acquired separately to produce the transmission profile.
The source and detector array in a conventional "3rd generation" CT system are rotated on a gantry within the imaging plane and around the object so that the angle at which the x-ray beam intersects the object constantly changes. A group of x-ray attenuation measurements from the detector array at a given angle is referred to as a "view", and a "scan" of the object comprises a set of views made at different angular orientations during one revolution of the x-ray source and detector. A conventional "4th generation" CT system is similar, except the detector array is a stationary ring that surrounds the patient and only the x-ray source rotates during the scan.
The scan data is processed to construct an image that corresponds to a two dimensional slice taken through the object. The prevailing method for reconstructing an image is referred to in the art as the filtered backprojection technique. This process converts the attenuation measurements from a scan into integers called "CT numbers" or "Hounsfield units", which are used to control the brightness of a corresponding pixel on a cathode ray tube display.
In order to acquire multiple slices during a single revolution of the gantry, it is common practice to provide a 2-dimensional detector array which has two or more rows of separate detector elements disposed along the Z dimension. The change from a linear to a 2-dimensional detector array requires a major alteration of the detector, the data acquisition system, the data communication and transfer system, as well as the data and image processing system. Such changes are costly, and once made, there is no easy way to revert back to a single slice data acquisition.